Method of and apparatus for measuring the correctness of and correcting an automatic test arrangement

ABSTRACT

A method of and an apparatus for determining the correctness of the calibration of an automatic test arrangement and correcting errors in the automatic test arrangement. The electrical length is determined from the tester driver of the automatic test arrangement to the socket pin of the tester interface unit, from the tester driver to a grounding point of the device under test, from the tester driver to the tester interface unit, and with the tester interface unit output pin connected to ground by a shorting block from the tester driver through the shorting block ground. The difference between the first electrical length and the second electrical length is compared with the difference between the first electrical length and the third electrical length, and the result is evaluated to determine the correctness of the calibration of the automatic test arrangement.

FIELD

[0001] The present invention pertains to automatic test arrangements forautomatic testing of devices. More particularly, the present inventionpertains to a method of and an apparatus for determining the correctnessof the calibration of an automatic test arrangement and a method of andapparatus for correcting the fundamental calibration errors inherent inautomatic test equipment, arrangements, and/or environments.

BACKGROUND

[0002] Newly manufactured products are generally tested prior to beingdelivered to customers in order to assure that the products perform asdesired. In high volume manufacturing of products, such as electroniccomponents, such acceptance testing is often performed by automatic testequipment. The test results, however, are only as good as thecalibration of the automatic test equipment. This is a problem ingeneral in acceptance testing, and it is a particular and fundamentalproblem in the acceptance testing of electronic components since theavailable operating speeds of such components are increasing, and thecomponent operating speed is often faster than the operating speed ofthe automatic test equipment. Methods of calibration presently used,known, and/or available are limited in accuracy and have associatedinherent errors. Consequently, in order to accurately evaluate andcorrect the results of testing by automatic test equipment, it isnecessary to determine the correctness of the calibration of theautomatic test equipment and to make and/or embed any modificationand/or corrections to the base tester calibration and/or the testresults that are necessary to obtain meaningful results.

[0003] The present invention is applicable to automatic test equipment,automatic test arrangements, and automatic test environments. In thefollowing, these will all be referred to as automatic test arrangements,but it is to be understood that equipment, arrangements, andenvironments are included, as well as other appropriate meanings.

[0004]FIG. 1 is a block diagram commonly considered to depict anautomatic test arrangement testing a device. Tester driver 10 applies atest signal to pin electronics card 12, the output of which is connectedto the input of tester interface unit 16. The output of tester interfaceunit 16 is connected to the device under test 20. Tester driver 10, andpin electronics card 12, might be a piece of general purpose automatictest equipment, while tester interface unit 16 is specifically adaptedfor testing of the particular device under test 20 on such a generalpurpose automatic test equipment.

[0005] The automatic test arrangement of FIG. 1 can test device undertest 20 by determining the electrical length of the signal path fromtester driver 10 to device under test 20, using time domainreflectometry. A signal is applied from tester driver 10, through pinelectronics card 12 and tester interface unit 16 to device under test20, and a resulting reflected signal is returned to tester driver 10.The time between initiation of the signal by tester driver 10 andreceipt of the reflected signal at tester driver 10 is used to determinewhether device under test 20 is acceptable, as is well known in the art.That time is referred to as the electrical length of the signal path.

[0006] In practice the automatic test arrangement is calibrated with nodevice connected to the output of tester interface unit 16. Thiscalibration electrical length is:

EL=PEC+TIU

[0007] where EL is electrical length, PEC is the electrical length ofpin electronics card 12, and TIU is the electrical length of testerinterface unit 16. This electrical length might be determined undervarious conditions. One condition is with no ground connections. Asecond is with the output of tester interface unit 16 connected toground by a grounding block. A third condition is with the output of pinelectronics card 12 connected to ground by a first grounding block andthe output of tester interface unit 16 connected to ground by a secondgrounding block. While each of these methods produces a calibrationvalue for the automatic test arrangement, the calibration values differ,and, in fact, none of them is wholly accurate because none of themconsiders all of the electrical lengths involved in the testarrangement. Nevertheless, these three conditions are frequently usedvariously to calibrate automatic test equipment.

[0008] The electrical length of the automatic test equipment made up oftester driver 10 and pin electronics card 12 is generally tested toobtain a first calibration value which might be stored in a memorydevice of the pin electronics card. Because not all electrical lengthsare considered, the measured value is the actual electrical length ofthe pin electronics card plus a calibration adjustment. One such valuemight be obtained and stored with the output of the pin electronics cardopen and another value obtained and stored with that output shorted toground.

[0009] A second set of calibrations is generally performed to determinethe electrical length of the pin electronics card and the testerinterface unit, both with the tester interface unit output open, andwith that output shorted to ground, and the resulting values might bestored in a memory device of the tester interface unit. Again, however,the measured values are the electrical length of the pin electronicscard and the tester interface unit plus a calibration adjustment. Evenso, these stored values do not properly reflect the calibration of theautomatic test arrangement because they do not take into considerationall the electrical lengths involved. Consequently, it is difficult tocorrectly calibrate an automatic test arrangement.

SUMMARY

[0010] The present invention pertains to automatic test arrangements forautomatic testing of devices. More particularly, the present inventionpertains to a method of and an apparatus for determining the correctnessof the calibration of an automatic test arrangement and a method of andan apparatus for correcting fundamental calibration errors inherent inan automatic test arrangement. Such an automatic test arrangementgenerally includes a tester driver, a pin electronics card having aninput connected to the tester driver and an output connected to anoutput pin such as pogo pin, and a tester interface unit having an inputconnected to the pin electronics card output pin and an output connectedto an output pin such as a socket pin. In accordance with the presentinvention, the electrical length from the tester driver to the socketpin is determined taking into consideration the pin electronics cardoutput pin and the tester interface unit output pin. The actualelectrical length from the tester driver, through the pin electronicscard, the pin electronics card output pin, the tester interface unit,and the tester interface unit output pin to a grounding point of thedevice under test is determined. In a first embodiment of the invention,a second electrical length is determined from the tester driver, throughthe pin electronics card and the pin electronics card output pin to thetester interface unit, with neither the pin electronics card output pinnor the tester interface unit output pin grounded. With the testerinterface unit output pin connected to ground by a shorting block, athird electrical length is determined from the tester driver, throughthe pin electronics card, the pin electronics card output pin, thetester interface unit, the tester interface unit output pin, and theshorting block to ground. A first difference value is determined as thedifference between the first electrical length and the second electricallength. A second difference value is determined as the differencebetween the first electrical length and the third electrical length. Athird difference value is determined as the difference between the firstdifference value and the second difference value, and the thirddifference value is evaluated to determine the correctness of thecalibration of the automatic test arrangement.

[0011] In another embodiment of the invention, a fourth electricallength is determined with the pin electronics card output pin connectedto ground by a first shorting block and the tester interface unit outputpin connected to ground by a second shorting block, the fourthelectrical length being from the tester driver, through the pinelectronics card, the pin electronics card output pin, the testerinterface unit, the tester interface unit output pin, and the secondshorting block to ground. A difference value is determined as thedifference between the first electrical length and the fourth electricallength. This difference value is subtracted from the first differencevalue, and that result is evaluated to determine the correctness of thecalibration of the automatic test arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] These and other aspects and advantage of the present inventionare more apparent from the following detailed description and claims,particularly when considered in conjunction with the accompanyingdrawings. In the drawings:

[0013]FIG. 1 is a block diagram commonly considered to depict anautomatic test arrangement testing a device;

[0014]FIG. 2 is a block diagram depicting an actual automatic testarrangement testing a device;

[0015]FIG. 3 is a flowchart of a first embodiment of a method ofdetermining the correctness of the calibration of an automatic testarrangement in accordance with the present invention;

[0016]FIG. 4 is a flowchart of a second embodiment of a method ofdetermining the correctness of the calibration of an automatic testarrangement in accordance with the present invention; and

[0017]FIG. 5 is a block diagram of a preferred embodiment of apparatusfor determining the correctness of an automatic test arrangement inaccordance with the present invention.

DETAILED DESCRIPTION

[0018]FIG. 2 is a block diagram of an automatic test arrangement inwhich a tester driver 10 applies a test signal to pin electronics card12, the output of which is connected to output pin 14. The input oftester interface unit 16 is connected to pin electronics card output pin14, while the output of tester interface unit 16 is connected to outputpin 18 which is connected to the device under test 20. By way ofexamples, output pin 14 from pin electronics card 12 might be a pogopin, while output pin 18 from tester interface unit 16 might be a socketpin. Tester driver 10, pin electronics card 12, and pogo pin 14 might bea piece of general purpose automatic test equipment, while testerinterface unit 16 and its socket pin 18 are specifically adapted fortesting of the particular device under test 20 on such a general purposeautomatic test equipment. The actual electrical length from testerdriver 10 to device under test 20 in FIG. 2 is given by:

EL(1)=PEC+Pogo _(—) c+TIU+Socket_(—) pin+Shortest return path toground  (1)

[0019] where Pogo-c is the electrical length of pogo pin 14 when it iscompressed, and Socket_pin is the electrical length of socket pin 18.

[0020] When the test arrangement is calibrated, the device under test 20is not connected, and instead the socket pin is left open. In thatconfiguration, the electrical length from tester driver 10 to socket pin18 is given by:

EL(2)=PEC+Cal _(—) adj _(—) o+{PEC+Pogo _(—) c+TIU−(PEC+Cal _(—) adj_(—) o)}  (2)

[0021] where Cal_adj_o is the previously determined calibrationadjustment value. TIU−(PEC+Cal_adj _o) might be stored in a memorydevice in tester interface unit 16.

[0022] With a shorting block connecting socket pin 18 to ground, theelectrical length from tester driver 10 to ground through the shortingblock is given by:

EL(3)=PEC+Cal _(—) adj _(—) o+{PEC+Pogo _(—) c+TIU+Socket _(—) pin+Shrt_(—) blk _(—) dut−PEC−Cal _(—) adj _(—) o}  (3)

[0023] where Shrt_(—) blk _(—) dut is the electrical length of theshorting block connected to socket pin 18.

[0024] With a first shorting block connecting pogo pin 14 to ground andsecond shorting block connecting socket pin 18 to ground, the electricallength from tester driver 14 to ground through the socket pin shortingblock is given by:

EL(4)={PEC+Pogo _(—) c+Shrt _(—) blk _(—) pogo+Cal _(—) adj _(—)s}+{PEC+Pogo _(—) c+TIU+Socket_(—) pin+Shrt _(—) blk _(—) dut−PEC −Pogo_(—) c−Shrt _(—) blk _(—) pogo−Cal _(—) adj _(—) s}  (4)

[0025] where Shrt_(—) blk _(—) pogo is the electrical length of theshorting block at pogo pin 14 and Cal _(—) adj_s is a previouslydetermined calibration adjustment value for the automatic testarrangement with shorting blocks on both pogo pin 14 and socket pin 18.

[0026] The values EL(1) through EL(4) are determined for an automatictest arrangement and are used to determine the correctness of thecalibration of the automatic test arrangement. FIG. 2 is a flowchart ofa first embodiment of a method of determining the correctness of thecalibration of an automatic test arrangement in accordance with thepresent invention. In step SI, the method is started. In step S2, thefirst electrical length is measured, utilizing equation (1). Then instep S3 the second electrical length is measured utilizing equation (2),and in step S4 the third electrical length is measured, using equation(3). In step S5, the second electrical length is subtracted from thefirst electrical length, giving:

Δ1=EL(1)−EL(2)=Socket _(—) pin+Shortest return path to ground  (5)

[0027] In step S6, the third electrical length is subtracted from thefirst electrical length, giving:

Δ2=EL(1)−EL(3)=Shortest return path to ground−Shrt _(—) blk _(—)dut  (6)

[0028] In step S7, the result of equation (6) is subtracted from theresult of equation (5), giving:

Δ3=Δ1−Δ2=Socket _(—) pin+Shrt _(—) blk _(—) dut  (7)

[0029] In step S8 this difference value is evaluated to determinewhether the automatic test environment is acceptable. The socket pinelectrical length is known from the socket specifications, while theelectrical length of the shorting block for the device under test can bedetermined by measurement of the size of the shorting block, with theelectrical length being, for example, 6 ps/mm×the socket length. Bycomparing this calculated electrical length with the result of equation(7), the correctness of the calibration of the automatic testenvironment can be determined. If the correctness is not satisfactory,then in step S9 adjustments, corrections, and/or improvements are made,and the process returns to step S2 to determine whether the result isacceptable. By way of example, tester driver 10, pin electronics card12, and/or tester interface unit 16 might be adjusted or their designimproved. If the correctness of the calibration, although not exact, isnevertheless within tolerances, corrections can be made to the resultsobtained during acceptance testing in order to obtain corrected results.Once an acceptable difference A3 is obtained in step S8, the method endsin step S10.

[0030]FIG. 3 is a flowchart of a second embodiment of a method fordetermining the correctness of the calibration of an automatic testenvironment in accordance with the present invention. The method of FIG.3 differs from the method of FIG. 2 in steps S6 and S7. In step S6 thefourth electrical length is subtracted from the first electrical length,giving:

Δ2′=EL(1)−EL(4)=Shortest return path to ground−Shrt _(—) blk _(—)dut  (8)

[0031] That result is then subtracted from the result of equation (5),giving:

Δ3′=Δ1−Δ2′=Socket _(—) pin+Shrt _(—) blk _(—) dut  (9)

[0032] Equations 6 and 8 are identical, and so equations 7 and 9 arealso identical. Thus, the method of FIG. 2 gives the same result as themethod of FIG. 3. The method of FIG. 3, however, requires an additionalshorting block for the pogo pin. In practice, for any given automatictest environment the decision of whether to use the method of FIG. 2 orthe method of FIG. 3 might be based on the method that gives thegreatest repeatability.

[0033] The calibration of an automatic test arrangement can bedetermined by the present invention. An automatic test equipment or atester interface unit can have the ability to determine Δ3 built in sothat the calibration of the arrangement can be checked when desired. Asdepicted in FIG. 5, the present invention can also be implemented by aproperly programmed automatic processing system 22 connected to theautomatic test environment 24.

[0034] Although the present invention has been described with referenceto preferred embodiments, various alternations, rearrangements, andsubstitutions can be made, and still the result would be within thescope of the invention.

What is claimed is:
 1. A method of determining the correctness of the calibration of an automatic test arrangement testing a device, the automatic test arrangement including a tester driver, a pin electronics card having an input connected to the tester driver and an output connected to a first output pin, and a tester interface unit having an input connected to the first output pin and an output connected to a second output pin, said method comprising with the second output pin connected to the device under test, determining a first electrical length from the tester driver to a grounding point of the device under test; with no connection to the second output pin, determining a second electrical length from the tester driver to the tester interface unit output; with the second output pin connected to ground by a shorting block, determining a third electrical length from the tester driver to the ground; determining as a first difference value the difference between the first electrical length and the second electrical length; determining as a second difference value the difference between the first electrical length and the third electrical length; determining as a third difference value the difference between the first difference value and the second difference value; and evaluating the third difference value to determine the correctness of the calibration of the automatic test arrangement.
 2. A method as claimed in claim 1, wherein the first electrical length is determined by determining the electrical length from the tester driver, through the pin electronics card, the first output pin, the tester interface unit, and the second output pin to a grounding point of the device under test.
 3. A method as claimed in claim 2, wherein the first electrical length is determined by applying an input signal from the tester driver, through the pin electronics card, the first output pin, the tester interface unit, and the second output pin to the device under test; receiving a signal as a result of reflection of the input signal from the device under test; and determining the elapsed time between application of the input signal and receipt of the reflected signal.
 4. A method as claimed in claim 1, wherein the second electrical length is determined by determining the electrical length from the tester driver, through the pin electronics card and the first output pin to the tester interface unit.
 5. A method as claimed in claim 4, wherein the second electrical length is determined by determining as a first value the sum of the electrical length of the pin electronics card and an adjustment value for the pin electronics card; determining as a second value the sum of the electrical lengths of the pin electronics card, the first output pin, and the tester interface unit; determining a third value by subtracting the first value from the second value; and adding the first value and the third value.
 6. A method as claimed in claim 1, wherein the third electrical length is determined with the second output pin connected to ground by a shorting block, by determining the electrical length from the tester driver, through the pin electronics card, the first output pin, the tester interface unit, the second output pin and the shorting block to ground.
 7. A method as claimed in claim 6, wherein the third electrical length is determined by determining as a first value the sum of the electrical length of the pin electronics card and an adjustment value for the pin electronics card; determining as a second value the sum of the electrical lengths of the pin electronics card, the first output pin, the tester interface unit, the second output pin, and the shorting block; determining a third value by subtracting the first value from the fourth value; and adding the first value and the third value.
 8. A method as claimed in claim 1, wherein the third difference value is evaluated by comparing the third difference value with the sum of the electrical lengths of the second output pin and the shorting block.
 9. A method of determining the correctness of the calibration of an automatic test arrangement testing a device, the automatic test arrangement including a tester driver, a pin electronics card having an input connected to the tester driver and an output connected to a first output pin, and a tester interface unit having an input connected to the first output pin and an output connected to a second output pin, said method comprising with the second output pin connected to a device under test, determining a first electrical length from the tester driver to a grounding point of the device under test; with no connection to the second output pin, determining a second electrical length from the tester driver to the tester interface unit output; with the first output pin connected to ground by a first shorting block and the second output pin connected to ground by a second shorting block, determining a third electrical length from the tester driver, to the ground; determining as a first difference value the difference between the first electrical length and the second electrical length; determining as a second difference value the difference between the first electrical length and the third electrical length; determining as a third difference value the difference between the first difference value and the second difference value; and evaluating the third difference value to determine the correctness of the calibration of the automatic test arrangement.
 10. A method as claimed in claim 9, wherein the first electrical length is determined by determining the electrical length from the tester driver, through the pin electronics card, the first output pin, the tester interface unit, and the second output pin to a grounding point of the device under test.
 11. A method as claimed in claim 10, wherein the first electrical length is determined by applying an input signal from the tester driver, through the pin electronics card, the first output pin, the tester interface unit, and the second output pin to the device under test; receiving a signal as a result of reflection of the input signal from the device under test; and determining the elapsed time between application of the input signal and receipt of the reflected signal.
 12. A method as claimed in claim 9, wherein the second electrical length is determined by determining the electrical length from the tester driver, through the pin electronics card and the first output pin to the tester interface unit.
 13. A method as claimed in claim 12, wherein the second electrical length is determined by determining as a first value the sum of the electrical length of the pin electronics card and an adjustment value for the pin electronics card; determining as a second value the sum of the electrical lengths of the pin electronics card, the first output pin, and the tester interface unit; determining a third value by subtracting the first value from the second value; and adding the first value and the third value.
 14. A method as claimed in claim 9, wherein the third electrical length is determined with the second output pin connected to ground by a shorting block, by determining the electrical length from the tester driver, through the pin electronics card, the first output pin, the tester interface unit, the second output pin and the shorting block to ground.
 15. A method as claimed in claim 14, wherein the third electrical length is determined by determining as a first value the sum of the electrical length of the pin electronics card and an adjustment value for the pin electronics card; determining as a second value the sum of the electrical lengths of the pin electronics card, the first output pin, and the first shorting block; determining as a third value the sum of the second value and an adjustment value for the second value; determining as a fourth value the sum of the electrical lengths of the pin electronics card, the first output pin, the tester interface unit, the second output pin, and the second shorting block; determining a fifth value by subtracting the first value from the fourth value; and adding the third value and the fifth value.
 16. A method as claimed in claim 9, wherein the third difference value is evaluated by comparing the third difference value with the sum of the electrical lengths of the second output pin and the shorting block.
 17. An article, comprising a storage medium having instructions stored thereon, the instructions when executed determining the correctness of the calibration of an automatic test arrangement testing a device, the automatic test arrangement including a tester driver, a pin electronics card having an input connected to the tester driver and an output connected to a first output pin, and a tester interface unit having an input connected to the first output pin and an output connected to a second output pin, by with the second output pin connected to the device under test, determining a first electrical length from the tester driver to a grounding point of the device under test; with no connection to the second output pin, determining a second electrical length from the tester driver to the tester interface unit output; with the second output pin connected to ground by a shorting block, determining a third electrical length from the tester driver to the ground; determining as a first difference value the difference between the first electrical length and the second electrical length; determining as a second difference value the difference between the first electrical length and the third electrical length; determining as a third difference value the difference between the first difference value and the second difference value; and evaluating the third difference value to determine the correctness of the calibration of the automatic test arrangement.
 18. An article as claimed in claim 17, wherein the instructions when executed determine the first electrical length by determining the electrical length from the tester driver, through the pin electronics card, the first output pin, the tester interface unit, and the second output pin to a grounding point of the device under test.
 19. An article as claimed in claim 18, wherein the instructions when executed determine the first electrical length by applying an input signal from the tester driver, through the pin electronics card, the first output pin, the tester interface unit, and the second output pin to the device under test; receiving a signal as a result of reflection of the input signal from the device under test; and determining the elapsed time between application of the input signal and receipt of the reflected signal.
 20. An article as claimed in claim 17, wherein the instructions when executed determine the second electrical length determined by determining the electrical length from the tester driver, through the pin electronics card and the first output pin to the tester interface unit.
 21. An article as claimed in claim 20, wherein the instruction when executed determine the second electrical length by determining as a first value the sum of the electrical length of the pin electronics card and an adjustment value for the pin electronics card; determining as a second value the sum of the electrical lengths of the pin electronics card, the first output pin, and the tester interface unit; determining a third value by subtracting the first value from the second value; and adding the first value and the third value.
 22. An article as claimed in claim 17, wherein the instructions when executed determine the third electrical length with the second output pin connected to ground by a shorting block, by determining the electrical length from the tester driver, through the pin electronics card, the first output pin, the tester interface unit, the second output pin and the shorting block to ground.
 23. An article as claimed in claim 22, wherein the instructions when executed determine the third electrical length by determining as a first value the sum of the electrical length of the pin electronics card and an adjustment value for the pin electronics card; determining as a second value the sum of the electrical lengths of the pin electronics card, the first output pin, the tester interface unit, the second output pin, and the shorting block; determining a third value by subtracting the first value from the fourth value; and adding the first value and the third value.
 24. An article as claimed in claim 17, wherein the instructions when executed evaluate the third difference value by comparing the third difference value with the sum of the electrical lengths of the second output pin and the shorting block.
 25. An article, comprising a storage medium having instructions stored thereon, the instructions when executed of determining the correctness of the calibration of an automatic test arrangement testing a device, the automatic test arrangement including a tester driver, a pin electronics card having an input connected to the tester driver and an output connected to a first output pin, and a tester interface unit having an input connected to the first output pin and an output connected to a second output pin, by with the second output pin connected to a device under test, determining a first electrical length from the tester driver to a grounding point of the device under test; with no connection to the second output pin, determining a second electrical length from the tester driver to the tester interface unit output; with the first output pin connected to ground by a first shorting block and the second output pin connected to ground by a second shorting block, determining a third electrical length from the tester driver, to the ground; determining as a first difference value the difference between the first electrical length and the second electrical length; determining as a second difference value the difference between the first electrical length and the third electrical length; determining as a third difference value the difference between the first difference value and the second difference value; and evaluating the third difference value to determine the correctness of the calibration of the automatic test arrangement.
 26. An article as claimed in claim 25, wherein the instructions when executed determine the first electrical length by determining the electrical length from the tester driver, through the pin electronics card, the first output pin, the tester interface unit, and the second output pin to a grounding point of the device under test.
 27. An article as claimed in claim 26, wherein the instructions when executed determine the first electrical length by applying an input signal from the tester driver, through the pin electronics card, the first output pin, the tester interface unit, and the second output pin to the device under test; receiving a signal as a result of reflection of the input signal from the device under test; and determining the elapsed time between application of the input signal and receipt of the reflected signal.
 28. An article as claimed in claim 25, wherein the instructions when executed determine the second electrical length by determining the electrical length from the tester driver, through the pin electronics card and the first output pin to the tester interface unit.
 29. An article as claimed in claim 28, wherein the instructions when executed determine the second electrical length by determining as a first value the sum of the electrical length of the pin electronics card and an adjustment value for the pin electronics card; determining as a second value the sum of the electrical lengths of the pin electronics card, the first output pin, and the tester interface unit; determining a third value by subtracting the first value from the second value; and adding the first value and the third value.
 30. An article as claimed in claim 25, wherein the instructions when executed determine the third electrical length with the second output pin connected to ground by a shorting block, by determining the electrical length from the tester driver, through the pin electronics card, the first output pin, the tester interface unit, the second output pin and the shorting block to ground.
 31. An article as claimed in claim 30, wherein the instructions when executed determine the third electrical length by determining as a first value the sum of the electrical length of the pin electronics card and an adjustment value for the pin electronics card; determining as a second value the sum of the electrical lengths of the pin electronics card, the first output pin, and the first shorting block; determining as a third value the sum of the second value and an adjustment value for the second value; determining as a fourth value the sum of the electrical lengths of the pin electronics card, the first output pin, the tester interface unit, the second output pin, and the second shorting block; determining a fifth value by subtracting the first value from the fourth value; and adding the third value and the fifth value.
 32. An article as claimed in claim 25, wherein the instructions when executed evaluate the third difference value by comparing the third difference value with the sum of the electrical lengths of the second output pin and the shorting block.
 33. Apparatus comprising: an automatic test arrangement including a tester driver, a pin electronics card having an input connected to the tester driver and an output connected to a first output pin, and a tester interface unit having an input connected to the first output pin and an output connected to a second output pin; a device to be tested; a shorting block; means for determining, with the second output pin connected to the device under test, a first electrical length from the tester driver to a grounding point of the device under test; means for determining, with no connection to the second output pin, a second electrical length from the tester driver to the tester interface unit output; means for determining, with the second output pin connected to ground by the shorting block, a third electrical length from the tester driver to the ground; means for determining as a first difference value the difference between the first electrical length and the second electrical length; means for determining as a second difference value the difference between the first electrical length and the third electrical length; means for determining as a third difference value the difference between the first difference value and the second difference value; and means for evaluating the third difference value to determine the correctness of the calibration of the automatic test arrangement.
 34. Apparatus as claimed in claim 33, comprising an automatic processing system.
 35. Apparatus comprising: an automatic test arrangement including a tester driver, a pin electronics card having an input connected to the tester driver and an output connected to a first output pin, and a tester interface unit having an input connected to the first output pin and an output connected to a second output pin; a device to be tested; a first shorting block; a second shorting block; means for determining, with the second output pin connected to the device under test, a first electrical length from the tester driver to a grounding point of the device under test; means for determining, with no connection to the second output pin, a second electrical length from the tester driver to the tester interface unit output; means for determining, with the first output pin connected to ground by the first shorting block and the second output pin connected to ground by the second shorting block, a third electrical length from the tester driver to the ground; means for determining as a first difference value the difference between the first electrical length and the second electrical length; means for determining as a second difference value the difference between the first electrical length and the third electrical length; means for determining as a third difference value the difference between the first difference value and the second difference value; and means for evaluating the third difference value to determine the correctness of the calibration of the automatic test arrangement.
 36. Apparatus as claimed in claim 35, comprising an automatic processing system. 